As a conventional conveyor device, there has been known a conveyor device including, in order to convey an object being conveyed by an optimum conveying force according to the weight and the like of the object being conveyed, a shaft having frame mounting parts at both ends thereof; a thrust bearing fixedly installed at a position on an inside from the frame mounting part on one end side of the shaft; a stopper fixedly installed at a position on an inside from the frame mounting part on the other end side of the shaft; a roller element supported on the shaft so as to be slidable in an axial direction of the shaft between the thrust bearing and the stopper and rotatable in a circumferential direction; a sprocket supported so as to be rotatable in the circumferential direction of the shaft between the thrust bearing and the roller element; a friction transmitting means for frictionally transmitting a rotational driving force of the sprocket to the roller element between the roller element and the sprocket; and a pressing means arranged between the stopper and the roller element to press the roller element toward the sprocket.
In this conveyor device, the pressing means is formed by a first pressing element being in contact with the roller element; a second pressing element arranged inside from the stopper so as to face the first pressing element; an elastic element arranged between the first pressing element and the second pressing element to urge both the pressing elements so as to separate them from each other; and an adjusting nut for moving the second pressing element in the axial direction with respect to the stopper (for example, refer to Patent Document 1).
Also, as another conveyor device, there has been known a conveyor device including a main shaft having frame mounting parts at both ends thereof; two fixing nuts threadedly engaged to fix the main shaft to a frame at a position on an inside from the frame mounting part; a sprocket integrally having a cylindrical chain shaft, the movement of which to the outside is regulated by a snap ring arranged on an inside from one fixing nut and which is rotatably supported on the main shaft; a roller fitted at an outer periphery of the chain shaft via a collared bush; a plate washer arranged contactingly so as to sandwich the side surface of the roller in cooperation with the collar of the bush; a thrust bearing being in contact with the plate washer; a spring for urging the thrust bearing so as to press the plate washer on the side surface of the roller; and an adjusting nut threadedly engaged with the main shaft on an inside from the other fixing nut to adjust a compression amount of the spring (for example, refer to Patent Document 2).
However, the conveyor device described in Patent Document 1 has a construction such that the first pressing element, the elastic element, the second pressing element, the adjusting nut threadedly engaged with the external threads of the second pressing element, the stopper, and the like are arranged outside the roller element in the axial direction of the shaft, a tool such as a spanner is brought close to the shaft from the vertical direction and connected thereto to rotate the adjusting nut, and the second pressing element is pressed on the first pressing element, thereby adjusting the rotational force (that is, the conveying force) of the roller element. Also, the conveyor device described in Patent Document 2 has a construction such that the thrust bearing, the spring, the adjusting nut, and the like are arranged outside the roller and the sprocket (chain shaft) in the axial direction of the main shaft, a tool such as a spanner is brought close to the main shaft from the vertical direction and connected thereto to appropriately rotate the adjusting nut, and thereby the holding force (frictional force) with which the plate washer and the collar of the bush hold the roller therebetween, that is, the rotational force (conveying force) of the roller is adjusted.
Therefore, the size in the axial direction of the shaft (or the main shaft) increases, which makes the size of the device large in the width direction. Also, since the rotational force (conveying force) is adjusted by a screw system using the adjusting nut, if the tightening amount of adjusting nut varies when a plurality of roller elements (or rollers) are adjusted, the rotational force (conveying force) may vary among the roller elements (or rollers). Also, although a tool such as a torque wrench can be used to restrain the variations, such a tool is expensive, so that the use thereof leads to an increase in running and maintenance costs. Further, in the adjusting work using a tool such as a spanner, operation such that after the adjusting nut is turned through a fixed angle, the spanner is removed once, and fitted again to the adjusting nut to turn the adjusting nut must be repeated, which poses a problem in that the adjusting work is troublesome, and therefore the adjusting work requires much time.    Patent Document 1: Japanese Unexamined Patent Publication No. 10-310219    Patent Document 2: U.S. Pat. No. 4,993,541, Specification